Moulding apparatus

ABSTRACT

A rotary turret injection moulding machine has a turntable (12) carrying a plurality of mould sets (17) and arranged to be rotated continuously, a device for injecting moulding material into the moulds and a clamping mechanism for holding the moulds closed during the injection being reciprocated in synchronsym with the rotation of the turntable. Each mould set has one part (18) firmly mounted on the turntable and another part (19) which pivots for opening and closing the mould. A cam (40) follower coupled to the movable part cooperates with a stationary cam (41) extending around the turntable axis to close and open the mould as the turntable is rotated. The movable mould part includes a mould plate mounted for tilting movement on its support arm, and dowel pins (30) and sockets (31) on the mould plates are arranged to ensure correct alignment when they are closed together.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to injection moulding apparatus, and inparticular, although not exclusively, to an injection moulding apparatusof the so-called rotary turret kind in which a plurality of mould setsare carried on a turntable, rotation of the turntable enabling the mouldsets to be moved successively to an injection station at which eachmould set is clamped firmly closed and molding material is injected intothe mould cavity.

2. The Prior Art

Rotary turret injection moulding machines in which the turntable isindexed around to bring the mould sets in turn to the injection stationare known. However, the turntables are driven intermittently, and thiscan cause problems, especially when there is a large number of mouldsets and a large mass is involved.

SUMMARY OF THE INVENTION

The present invention provides a solution to this problem. In accordancewith a first aspect of the invention, an injection moulding apparatuscomprises a turntable, drive means for continuously rotating theturntable, a plurality of mould sets carried on the turntable, and aclamping and injecting assembly including means for clamping each mouldset closed and means for injecting moulding material into the clampedmould set, the clamping and injecting assembly being mounted forreciprocal movement along an arcuate path in synchronism with therotation of the turntable.

With such an arrangement the difficulties encountered in repeatedlystarting and stopping rotation of a turntable having large inertia areavoided, the clamping and injecting assembly which may havecomparatively small inertia being driven instead.

In a preferred construction the turntable rotates about a central shaftand the clamping and injecting assembly includes a support member and anarm journalled on the shaft and connected to the support member forguiding the member concentrically with the turntable duringreciprocation of the clamping and injecting assembly.

To facilitate synchronous movement of the clamping and injectingassembly with the turntable it is expedient for latching means to beprovided for latching the clamping and injecting assembly to theturntable to be moved therewith during a forward stroke, means beingprovided for driving the clamping and injecting assembly in the oppositedirection through a return stroke.

In known injection moulds the mould parts which form the mould cavityare generally guided for movement towards and away from each other byguide rods which extend between them. The guide rods are inconvenientbecause they impede access to the opened mould, whereby removal of themoulded articles is hindered.

In accordance with a second aspect of the invention a simple answer tothis problem is achieved by an injection moulding apparatus comprisingfirst and second mould parts movable relative to each other between openand closed positions, said mould parts defining a mould cavity in theclosed position thereof, and the first mould part being mounted on asupport characterised in that the second mould part is arranged to pivotabout an axis fixed with respect to the first mould part during saidmovement between the open and closed positions of the mould parts.

A pivotal connection between the mould parts enables the movable part tobe displaced easily to an open position in which it is substantiallyclear of the other part, whereby unimpeded removal of the mouldedarticles from the mould is facilitated. It is preferable that themovable part be capable of rotating through at least about 90° betweenthe open and closed positions.

As mentioned above, in known injection moulds the parts which form themould cavity are generally guided for movement towards and away fromeach other by guide rods. In order to ensure that the parts will closeproperly together they must be accurately aligned. Even a smallmisalignment can result in the moulded articles being unacceptable andhaving to be rejected.

In accordance with a third aspect the present invention proposes asolution to this problem by providing an injection moulding apparatuscomprising a mould set including two members movable relative to eachother between an open position and a closed position defining a mouldcavity, characterised in that one of said mould members is capable oftilting movement relative to the other member as the members are broughttogether into the closed position, and guide means are provided on themould members and engage as the mould members are moved into the closedposition to ensure correct alignment between said members.

A mould set of this construction has the advantage that the mouldmembers are guided automatically into correct alignment each time themould is closed without requiring fixed guide rods extending betweenthese members. This form of mould is of particular benefit when themould members are not moved rectilinearly between the open and closedpositions, such as when they are connected for relative pivotal movementin accordance with the preceding aspect of the invention.

In accordance with a fourth aspect the present invention provides aninjection moulding apparatus comprising a turntable, drive means forrotating the turntable, a plurality of mould sets carried on theturntable, and means for opening and closing the mould sets,characterised in the mould opening and closing means includes stationarycam means extending around the turntable axis, and cam followers coupledto the respective mould sets and arranged to co-operate with the cammeans to open and close each mould set in accordance with apredetermined sequence of operations as the turntable is rotated.

The use of a cam system to open and close the moulds allows theapparatus to be simplified since it obviates the need for fluid actuateddevices having to be carried on the turntable with the mould sets, andalso the need for fluid flow lines for conducting pressurised fluid toand from such device. Thus in a preferred construction the cam means isresponsible for holding the mould sets closed during rotation of theturntable, except at the injecting station where an increased clampingforce is applied by an actuator supported independently of the mouldsets.

The stationary cam means proposed by the invention are especiallysuitable for an apparatus in which the mould sets have one part firmlymounted to the turntable and another part pivotable relative thereto inaccordance with the second aspect of the invention mentioned above.

The different aspects of the invention as mentioned above may beconveniently combined in a rotary turret injection moulding machine ofuncomplicated construction and which is efficient and reliable inoperation.

A better understanding of the above and other novel features provided bythe invention will be had from the following detailed description of apresently preferred embodiment, reference being made to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a rotary turret injection moulding machineaccording to the invention;

FIG. 2 is a vertical section through the machine;

FIG. 3 is a detail plan view showing one of the mould assemblies;

FIG. 4 is a side view of the mould assembly shown in FIG. 3, and

FIGS. 5 and 6 are views from opposite sides showing an injection deviceof the machine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The illustrated injection moulding machine has a stationary frame 1supporting a rotor assembly for rotation about a vertical axis. Therotor assembly includes a hollow shaft 2 journaled in the frame bybearings 3. The shaft is rotated by a drive unit 4 mounted on the frame1 and coupled kinematically to the shaft through a gear 5 and an endlesschain 7 trained around the gear 5 and a sprocket 8 fast with the saft 2.A chain tensioner 9 is provided to maintain constant tension in thechain 7. Fast with the upper end of shaft 2 is a drive plate 10 with aninner hub portion connected to an outer ring by radial spokes. The outerring of the drive plate is coupled to an annular turntable 12 byvertical tie rods 13 located at the ends of the spokes for the turntableto be driven around with the shaft 2. The turntable is supported in ahorizontal plane by sets of rollers spaced apart around the frame 1. Theroller sets include vertical rollers 14 arranged to contact the innerperiphery of the annular turntable 12, and conical rollers 15 mountedwith their axes inclined slightly to the horizontal for supporting theturntable from below. With this construction the rotor shaft is notrequired to support the full weight of the turntable 12 and those partscarried on it; as described below, and with the conical supportingrollers 15 the turntable has a natural self-centering tendency as it isrotated around on the frame 1.

Uniformly spaced apart around the outer periphery of the turntable 12are notches 16, the purpose of which will be explained below, andmounted on the turntable adjacent each notch is a respective mould set17. As may be best seen in FIGS. 3 and 4, each mould set includes alower mould part 18 and an upper mould part 19. The part 18 includes abase plate 20 fixed on the turntable, and a bottom mould plate 21secured on the base plate 20 with a member 23 of thermally insulatingmaterial located between them. Attached to the base plate are a pair ofside plates 24 in which the opposite ends of a fulcrum pin 25 arejournaled by bearings. The upper mould part 19 includes a pair of arms26 carried on and keyed to the pin 25 and clamped to it by means ofscrews. At their free ends the arms 26 carry a top mould plate 22 whichco-operates with the bottom plate 21 to define the mould cavity, or inthe case of the illustrated embodiment a pair of annular cavities 27.The plate 22 is not secured rigidly to the arms 26, but is capable ofsome translational and tilting movement. The connection between theplate 22 and each arm 26 is effected by a screw 28 which is adjusted topermit some movement between the plate and arm, and a belleville spring29 is inserted between the plate 22 and arm 26. The pivotal mountingbetween the upper and lower mould parts 18, 19, allows the top plate 22of the mould to be moved between a closed position surmounting thebottom plate 21, as shown in FIGS. 3 and 4 and the left hand side ofFIG. 2, and an open position displaced at 90° to the closed position andin which it is moved clear of the bottom plate as seen at the right handside of FIG. 2. The spring mounting of the top plate on the arms 26enables it to be brought into correct alignment with the bottom plateeach time the mould is closed, and to ensure that the plates becomealigned automatically, the bottom plate is equipped with a pair of dowelpins 30 having tapered upper ends, and the top plate is provided withsockets fitted with ring inserts 31 to receive the dowel pins. Thus, asthe mould plates 21, 22 close together the dowel pins 30 enter the rings31 thereby adjusting the position of the top plate 22 to registerprecisely with the bottom plate 21.

To move the upper mould part 19 between the open and closed positions, alever 33 is keyed for rotation with the fulcrum pin 25. The lever 33consists of a pair of parallel arms of L-shape which are interconnectedat their free ends by a thrust block 34. A second lever 35 is pivotedbetween the arms of lever 33 on a pin 36 parallel to, but spaced fromthe pin 25. A strong coil compression spring 38 is inserted between thelever 35 and the thrust block and normally urges the lever 35 against astop 39 fixed to the lever 33. At its free end the lever 35 carriesrollers 40 which co-operate with a cam track 41 which is fixed on theframe 1 of the injection moulding machine and extends continuouslyaround the axis of the rotor. The cam track is designed so that, as themould sets 17 travel around on the turntable 12, they are opened andclosed in accordance with a predetermined sequence of operations. When amould is to be held open the cam track 41 maintains the lever 35 andhence lever 33 in a generally horizontal position as shown at the righthand side of FIG. 2, and when the mould is to be closed an inclinedsection of the cam track designated 42 in FIG. 1 moves the levers 35, 33to a generally vertical position, as shown at the left hand side of FIG.2. To ensure that the mould is clamped tightly closed the cam track isadapted to push the end of lever 35 radially outwardly so that thespring 38 is compressed and the full force of this spring acts throughthe lever 33 and arms 26 to hold the top plate 22 firmly against thebottom plate 21. A further inclined cam track section designated 43 inFIG. 1 adjusts the moulds from the closed position to the open position.

The mould plates 20, 21 include passages 45 for circulation of thermalfluid to stabilise the mould temperature and accelerate curing of themoulding material in the mould. The particular fluid will be chosen inaccordance with temperature requirements. It could be cooling water inthe case of thermoplastic moulding material, or it could be steam or asdescribed below in the exemplary embodiment, hot water as the mouldingmaterial is thermosetting. For conducting the water to and from themould plates annular inlet and outlet manifolds 50 and 51, respectively,are included in the rotor assembly and are mounted on the drive plate 10by means of brackets 52. The manifolds 50, 51 are connected to the mouldplates by pipelines 54 and are respectively connected to centrallylocated inlet tank 55 and outlet tank 56 by hoses 57. The tanks aresupported on the rotor shaft 2 and are separated by a spacer 58. Hotwater is fed to the inlet tank 55 by means of a rotary union 59, and thecooled water is discharged from the outlet tank 56 via a pipe 61extending down through the centre of shaft 2, and a rotary union 62.From the foregoing it will be appreciated that the hot water circulatescontinuously, the flow path being inlet tank 55, inlet manifold 50,mould plates 21, 22, outlet manifold 51 and outlet tank 56. If it isrequired that water should be supplied to the mould plates only duringpart of the machine cycle, valves may be included in the pipelines 54and can be operated by means of cams mounted on the machine frame.

At the injection station of the moulding machine there is provide aclamping and injection assembly supported for reciprocal movement alongan arcuate path centered on the axis of the machine rotor. A curvedcarrier plate 60 rests on support rollers 62 mounted on the machineframe 1, and a radial arm 64 journaled on the rotor shaft 2 andconnected to the carrier plate by a pair of vertical tie bars 65constrains the carrier plate 60 to move concentrically with theturntable 12. A fluid actuated ram 66 is coupled between the frame 1 andone of the tie bars 65 for effecting a return stroke of the carrierplate which is in the clockwise direction as seen in FIG. 1.

Mounted on the carrier plate 60 is a latching device comprising a fluidcylinder 67 and a latching key 68 connected to the piston rod of thecylinder. The cylinder is actuable to advance and retract the key 68 toengage and disengage the notches 16 formed in the periphery of theturntable 12. When the latch is engaged, the carrier plate becomeslocked with the turntable and is driven around with it to perform aforward stroke of the clamping and injection assembly. When the latch isreleased the carrier plate 60 is freed to undergo a return stroke underthe action of the ram 66.

Also mounted on the carrier plate 60 is a clamping mechanism forexerting an increased closing force on each mould set as the mouldingmaterial is injected into the mould cavities. The clamping mechanismincludes a pair of generally C-shaped brackets 70 each supported by apair of parallel links 71, 72 pivoted to a vertical plate 73 upstandingfrom a mounting p late 74 which is fixed to the carrier plate 60. Thevertical plates 73 and brackets 70 are spaced apart on either side ofthe latching mechanism 67, 68 as may be seen in FIG. 1. The upper links72 are fashioned as levers and at their ends opposite the brackets 70carry rods 75 which are urged downwardly by springs 76 acting betweenthe ends of the rods and stops fixed on plates 73. A clamping member 78of generally U-shaped cross-section is carried by the brackets 70 and anupper limb of this member is arranged to extend over the turntable 12for engaging the upper parts 19 of the mould sets. The lower limb ofmember 78 supports a fluid actuator 80 which is operable to push apressure plate 81 up against the under-side of the turntable 12. Thus,when the actuator 80 is activated, the pressure plate is pushed up toengage the turntable, and the reaction force causes the clamping member78 to be pulled downwardly to engage the top of the mould set and thetwo mould plates 21, 22 become clamped tightly together under the fullforce of the actuator 80. The high clamping pressure applied by theactuator 80 holds the mould plates securely closed during injection ofthe moulding material into the mould cavities, it being essential toprevent parting of the mould plates at this stage if flash on themoulded plates is to be avoided. When the full clamping pressure is tobe released, the pressure plate 81 is retracted by the actuator 80 andthe clamping member 78 is lifted slightly under the action of springs 76so as to be raised clear of the mould set. It will be appreciated thatthe clamping member 78 has an opening to enable the latching key 68 tomove into co-operation with the turntable and this opening, or a furtheropening, allows an injection nozzle to be moved into co-operation withthe clamped mould set. The injection device has been omitted in FIGS. 1and 2 for reasons of clarity, but is clearly illustrated in FIGS. 5 and6. It comprises a vertical support 84 extending upwardly from and fixedto the carrier plate 60. Pivoted to the upper end of the support 84 inthe manner of a pendulum is a member 85 which swings in a plane radialto the axis of the machine rotor and bisecting the high pressureclamping mechanism. The lower end of the member 85 carries the injectionnozzle 86 and a control valve 87 to control supply of moulding materialto the nozzle. The material is fed to the upper end of member 85 andpasses down through this member to the control valve. The member can forexample be constructed as a mixer for mixing the moulding material onits way to the injection nozzle and can include a temperature controljacket. The member 85 can also be designed to perform other operationsto suit the particular material being used. For pivoting the member 85to move the nozzle 86 into and out of engagment with a clamped mould seta double acting fluid cylinder 88 is connected between a bracket on thesupport 84 and an arm 89 fast with the member 85. When the cylinder 88is retracted the nozzle is withdrawn, and when the cylinder is extendedthe nozzle is swung forward into engagement with a mould, as seen inFIGS. 5 and 6.

A control system is provided to ensure synchronised operation of themachine, including the reciprocation of the clamping and injectionassembly, the actuation of the fluid actuators 66, 67, 80 and 88, andthe operation of the control valve 87. The control system includes amould sensor 90 for sensing when a mould set is in correct position tobe clamped by the clamping mechanism, micro-switches 91 for sensing theend positions of the carrier plate movement, and an electrical controlunit 92. Control valves for the fluid actuators are included in afurther control box 93 also mounted on the machine frame.

Operqtion of the described rotary turret moulding machine will now beexplained by reference to the various steps involved in the cycle of onemould set. It will be understood that all the mould sets perform thesame cycle but clearly the times at which the different steps arecarried out will be staggered and will depend on the relative positionsof the mould sets. The particular mould set will be assumed to beinitially at the 3 o'clock position as viewed in FIG. 1. In thisposition, the mould is fully open as shown at the right hand side ofFIG. 2. The turntable 12 is rotated continuously at a constant speed bythe drive unit 4 and moves around counter clockwise as seen in FIG. 1.During the first 90° of rotation from the assumed initial position themould remains fully open and cleaning operations can be performed on themould plates 21, 22. Also, while the mould is open, any inserts to beincluded in the moulded articles should be loaded into the mould cavity.As rotation of the turntable 12 continues, the mould set approaches theinclined cam track section 42 which by acting on the lever 35 closes theupper mould part 19 down on the lower part 18 and clamps the mouldplates closed under the force of spring 38. Full closure of the mould isachieved shortly before the mould reaches the injection station at aposition diametrically opposite the initial position. Arrival of themould set at said position is detected by the sensor 90, which actuallyworks by sensing the immediately following mould set, and in response toa signal from the sensor 90 the control system actuates the cylinder 67of the latching mechanism to engage the key 68 in the adjacent notch 16of the turntable so that the carrier plate, and hence the clamping andinjction assembly, become locked to the turntable 12 and start to movearound with it. As soon as the latch has engaged, the actuator 80 isactivated so that the mould set becomes clamped under high pressurebetween the clamp member 78 and the pressure plate 81. Next, thecylinder 88 is actuated to bring the injection nozzle 86 intoco-operation with the inlet orifice of the mould set, and the controlvalve is opened for a preset time to inject a predetermined quantity ofthe moulding material into the cavities of the mould. The injection ofmaterial is completed during a small angle of rotation of the turntable,which in the illustrated embodiment is less than 10°, and before thecarrier plate reaches the end of its forward stroke as determined by themicroswitches 91. When this end position is reached the injection nozzle86 is withdrawn by means of cylinder 88, the clamping pressure exertedon the mould set by actuator 80 is released so that the clampingmechanism disengages the mould set, the latching key 68 is retracted,and the ram 66 is actuated to return the carrier plate to its oppositeend position ready for the next following mould set to be clamped andinjected with moulding material.

Although the material is not fully cured when the high clamping pressureis removed, it still remains closed under the reduced closing forceexerted by the spring 38. The hot water flowing through the passages inthe mould plates 21, 22 accelerates the curing process and by the timethe mould set reaches the inclined cam track section 42 the materialwill be set sufficiently to be handled. The inclined cam track section43 effects opening of the mould, the upper part 19 of the mould beingmoved upwardly and inwardly away from the lower part 18 to facilitateunobstructed removal of the finished articles. The mould set has thentravelled through 360° and the described cycle is repeated.

A moulding machine as described above has been constructed and testedand has proved highly successful in the manufacture of rings of siliconerubber. Because the clamping and injection assembly is arranged to moveto and fro synchronously with rotation of the turntable, the turntablecan be rotated continuously and problems associated with intermittentdrive of a rotor with large inertia is avoided. By providing means tohold the moulds closed under spring force, a single high pressureclamping device can be employed to act on each mould set duringinjection of material and the machine construction is therebysimplified. The pivotal connection of the mould parts, as well as thespring mounting of the top mould plates contribute to the convenience ofthe machine by allowing unobstructed access to the opened moulds.

Modifications to the machine are, of course, possible without departingfrom the scope of this invention. For example, while the turntable hasbeen described as having a gear and chain drive it will be understoodthat any mechanism capable of imparting continuous rotation to theturntable could be used. In addition, instead of being assembled from anumber of parts the mould carriers could be of integral construction,such as cast members. Thus the parts 20, 24 may be combined in onecasting and the arms 26 and parts 33 combined in another casting.Furthermore, the spring 38 could be arranged to act between the arms 26and a lateral projection provided on the lever 35 and overlying the arms26.

It is not important that the injection nozzle should be supportedpivotally to be moved in a vertical plane as shown in FIGS. 5 and 6 andother arrangements are possible. All that is required is that the nozzleshould be able to move into and out of engagement with each mould set,and it could alternatively be arranged to be pivoted in a horizontalplane or to be moved linearly in the radial direction.

Other modifications are also possible and will occur to skilled readers.

I claim:
 1. An injection moulding apparatus comprising a turntable,drive means for continuously rotating the turntable, a plurality ofmould sets carried on the turntable, a clamping and injecting assemblyincluding means for clamping each mould set closed and means forinjecting moulding material into the mould set while clamped closed bythe clamping means, and means mounting the clamping and injectingassembly for reciprocal movement along an arcuate path in synchronizmwith the rotation of the turntable.
 2. An apparatus according to claim1, including a central shaft mounting said turntable, said central shaftdefining a rotation axis, said turntable being rotatable about saidrotation axis of said central shaft, and the clamping and injectingassembly includes a support member and an arm, said arm having a firstend journalled for rotation about said rotation axis of said centralshaft and a second end attached to said support member for guiding theclamping and injecting assembly for movement concentric with theturntable.
 3. An apparatus according to claim 1, wherein latching meansis provided for latching the clamping and injecting assembly to theturntable for movement therewith during a forward stroke of saidassembly, and means is provided for moving the clamping and injectingassembly through a return stroke when the latching means is disengaged.4. An apparatus according to claim 1, wherein said turntable is annularand is freely supported by rollers mounted on a stationary frame andspaced apart around the turntable, said rollers being conical and soarranged that the turntable is self-centering during rotation thereof.5. An apparatus according to claim 1, wherein each said mould setcomprises first and second mould parts which are movable relative toeach other between open and closed positions, said mould parts defininga mould cavity in the closed position thereof, the first mould partbeing fixedly mounted on said turntable and the second mould part beingpivotable about an axis fixed with respect to the first mould partduring said movement between the open and closed positions of the mouldparts.
 6. An apparatus according to claim 5, wherein said second mouldpart is pivotable through an angle of about 90° or greater in movingfrom the closed position to the open position.
 7. An apparatus accordingto claim 5, wherein said second mould part is capable of tiltingmovement relative to the first mould part as said mould parts arebrought together into the closed position, and guide means are providedon said mould parts and engage as the mould parts are moved into theclosed position to ensure correct alignment between said mould parts. 8.An apparatus according to claim 7, wherein the guide means comprisesprojections on said first mould part and sockets for receiving theprojections in said second mould part.
 9. An apparatus according toclaim 7, wherein said second mould part is carried on a pivoting arm ina manner permitting limited translational and tilting movementtherebetween, and spring means is provided between said second mouldpart and said arm for urging said second mould part generally towardsthe first mould part.
 10. An apparatus according to claim 1, includingmeans for opening and closing the mould set, said means for opening andclosing the mould sets including stationary cam means extending aroundthe turntable axis and cam followers coupled to said respective mouldsets and arranged to cooperate with the cam means to open and close eachmould set in accordance with a predetermined sequence of operations asthe turntable is rotated.
 11. An apparatus according to claim 10,wherein said cam means is arranged to close each mould set as itapproaches an injection station and to maintain the mould set closed forsufficient time to allow the injected material to cure after leaving theinjection station, the clamping means comprising a device for clampingeach mould set tightly closed under an increased clamping force duringinjection of moulding material into the mould cavity thereof.
 12. Anapparatus according to claim 10, wherein the cam follower is coupled tosaid second mould part of each mold set through spring means, wherebythe cam means holds the mould parts closed under a predetermined springforce.